Question

Identify highest field strength ligand from following.

• A. $\text{H}_2\text{O}$
• B. EDTA
• C. en
• D. $\text{S}^{2-}$

Hint:

A great rule of thumb for the spectrochemical series is checking the donor atom type: $\text{Halogen/Sulfur donors} < \text{Oxygen donors} < \text{Nitrogen donors} < \text{Carbon donors}$. Since "en" binds via nitrogen atoms, it beats out the oxygen and sulfur options instantly!

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The problem asks us to determine which of the four given ligands possesses the highest field strength according to the spectrochemical series.

Step 2: Detailed Explanation:
The spectrochemical series is an experimentally determined sequence that ranks ligands based on their ability to split the d-orbitals ($\Delta_o$, crystal field splitting energy) in coordination complexes. The general order of increasing field strength for common ligands is: $$ \text{I}^- < \text{Br}^- < \text{S}^{2-} < \text{SCN}^- < \text{Cl}^- < \text{F}^- < \text{OH}^- < \text{C}_2\text{O}_4^{2-} < \text{H}_2\text{O} < \text{NCS}^- < \text{EDTA} < \text{NH}_3 < \text{en} < \text{NO}_2^- < \text{CN}^- < \text{CO} $$ Let's look at where our given options sit in this series:

• $\text{S}^{2-}$ is a weak-field halide/sulfide donor ligand.

• $\text{H}_2\text{O}$ sits intermediate on the boundary line.

• EDTA is a hexadentate chelating ligand lying above water.

• en (ethylenediamine) is a strong-field bidentate nitrogen-donor ligand that sits significantly higher than EDTA, $\text{H}_2\text{O}$, and $\text{S}^{2-}$.
Therefore, among the options provided, ethylenediamine (en) induces the maximum crystal field splitting.

Step 3: Final Answer: The highest field strength ligand among the choices is en, which corresponds to option (C).